1. Field of the Invention
The present invention relates to a liquid chromatograph having a mobile phase flow passage for sending a mobile phase obtained by mixing a plurality of kinds of solvents with a mixer and used for introducing a sample injected from a sample injection portion into an analysis column. Particularly, the present invention relates to a liquid chromatograph having a trapping column for concentrating a dilute sample and allowing the sample to be analyzed in a concentrated state.
2. Description of the Related Art
Generally, in the case of analysis using a high-performance liquid chromatograph, a sample is injected into an analysis flow passage from a sample injection portion, and then transferred into an analysis column by a mobile phase sent by a liquid sending pump, and then separated into individual components by the analysis column. At this time, when the amount of the sample injected from the sample injection portion is large, a sample band in the analysis column is broadened by the action of a solvent contained in the sample, thereby reducing separation performance and making it impossible to achieve highly-sensitive analysis. For this reason, it is not preferred that a large amount of sample solution is injected from the sample injection portion.
However, in the case of analysis of a dilute sample, it is necessary to increase the absolute mass of the sample to achieve sufficient sensitivity, and therefore there is a case where a large amount of sample must be injected from the sample injection portion. In such a case, analysis involving online concentration using a trapping column is often carried out.
In the case of analysis involving online concentration, a sample injected from the sample injection portion is concentrated by trapping it in the trapping column, and then the concentrated sample trapped in the trapping column is separated by an analysis column and analyzed. In this case, in order to examine the concentration efficiency of the trapping column and the degree of deterioration of the analysis column, the same sample is also subjected to normal analysis (i.e., direct analysis) not involving online concentration, and then the results of both analyses are compared to determine a recovery rate. In order to carry out direct analysis to determine the recovery rate, it is necessary to change the flow passage configuration of a liquid chromatograph from a flow passage configuration for online concentration to a flow passage configuration for direct analysis. Such a change in flow passage configuration is very complicated and takes much time, and in addition, attention needs to be paid so that leakage of a mobile phase and a dead volume in a flow passage will not occur even after changing a flow passage configuration. In order to solve such a problem, the present inventor has proposed a liquid chromatograph having flow passage switching valves (see US 2005/0167348 A1). In the liquid chromatograph, a flow passage configuration can be switched between a flow passage configuration for online concentration and a flow passage configuration for direct analysis only by operating the flow passage switching valves.
Meanwhile, liquid chromatographic analysis is carried out using a mobile phase obtained by mixing two or more kinds of solvents, and the mixing ratio between/among the solvents is changed with time. Therefore, in order to promote the mixing of the solvents, a mixer is provided in a flow passage. In such liquid chromatographic analysis, in some cases, a mobile phase is preferably sent at a conventional flow rate of about 50 μL/min to 1 mL/min, and in other cases, a mobile phase is preferably sent at a micro flow rate of 50 μL/min or less.
For example, in the case of direct analysis, a mobile phase is generally sent at a conventional flow rate, but in the case of concentration analysis after sample concentration, a mobile phase is generally sent at a micro flow rate. In a case where a mobile phase is sent at a conventional flow rate, mixing of the mobile phase is preferably promoted using a mixer having a relatively large capacity of about 1 mL. On the other hand, in a case where a mobile phase is sent at a micro flow rate, mixing of the mobile phase is preferably promoted using a mixer having a relatively small capacity of about 5 μL. This is because, in a case where a mixer having a capacity of 1 mL is used when a mobile phase is sent at a flow rate of 5 μL/min, the capacity of the mixer is too large for the flow rate of the mobile phase and therefore a delay as long as about 200 minutes occurs. On the other hand, in a case where a mixer having a capacity of 5 μL is used when a mobile phase is sent at a flow rate of 1 mL/min, the mobile phase cannot be sufficiently mixed. For this reason, in a case where it is necessary to send a mobile phase at various flow rates in a wide range from a micro flow rate to a conventional flow rate in a single system of a liquid chromatograph, the selection of the capacity of a mixer to be used becomes a problem.